If you hold down the shift key while typing a cursor motion command, this sets the mark before moving point, so that the region extends from the original position of point to its new position. This feature is referred to as shift-selection. It is similar to the way text is selected in other editors.
The mark set via shift-selection behaves a little differently from what we have described above. Firstly, in addition to the usual ways of deactivating the mark (such as changing the buffer text or typing
C-g), the mark is deactivated by any unshifted cursor motion command. Secondly, any subsequent shifted cursor motion command avoids setting the mark anew. Therefore, a series of shifted cursor motion commands will continuously adjust the region.
Shift-selection only works if the shifted cursor motion key is not already bound to a separate command (see Customization). For example, if you bind
S-C-f to another command, typing
S-C-f runs that command instead of performing a shift-selected version of
A mark set via mouse commands behaves the same as a mark set via shift-selection (see Setting Mark). For example, if you specify a region by dragging the mouse, you can continue to extend the region using shifted cursor motion commands. In either case, any unshifted cursor motion command deactivates the mark.
To turn off shift-selection, set
nil. Doing so does not disable setting the mark via mouse commands.